DEFINITION AND NATURE OF NEUROPSYCHOLOGY
The term “neuropsychology” was used as a subtitle in Donald Hebb’s influential book The organization of behavior: A neuropsychological theory, published in 1949, although the term itself was not defined. With the demise of behaviorism and renewed interest in cognitive processes in the 1950s and 1960s, the term appeared with increasing frequency, although its definition remained vague and was used in different senses by different people. Although, as you will see, researchers had been interested in the effects of brain damage and disease on behavior for many years, it was arguably sometime after behaviorism’s fall from grace that neuropsychology came to develop a distinct identity within psychology, and its parameters were further clarified by the publication of the first edition of Kolb and Whishaw’s Fundamentals of human neuropsychology and Lezak’s Neuropsychological assessment in 1980 and 1983 respectively.
Neuropsychology is usually broadly defined as the study of brain-behavior relationships. Of course, this definition does not capture the multiplicity of questions and approaches that have been used to explore how the central nervous system represents, organizes, and generates the infinite range of human capabilities and actions. Modern neuropsychology includes the study of the classic problems of psychology—attention, learning, perception, cognition, personality, and psychopathology—using techniques that include the methods of experimental psychology as well as the methodologies of test construction and psychometrics.
Its scientific palate includes such state-of-the-art technologies as high-resolution structural and functional neuroimaging and other techniques such as computational modeling, and it is beginning to be integrated with genomics and other advanced biological technologies such as proteomics and metabolomics.
According to a consortium of representatives of a number of professional neuropsychological organizations that convened in 1997 in Houston, Texas, clinical neuropsychology can be defined as “the application of assessment and intervention principles based on the scientific study of human behavior across the lifespan as it relates to normal and abnormal functioning of the central nervous system” (Hannay et al., 1998). In practice, this translates into using standardized psychological tests, which are usually designed to assess various aspects of human cognition, ability, or skill, to provide information to a variety of clinical questions about the central nervous system and behavior. Less often, tests of personality or affective behavior have been adapted as neuropsychological instruments.
The human brain is a fascinating and enigmatic machine. Weighing only about 3 pounds (1.36 kilograms) and with a volume of about 1,250 cubic centimeters, it has the ability to monitor and control our basic life support systems, to maintain our posture and direct our movements, to receive and interpret information about the world around us, and to store information in a readily accessible form throughout our lives. It allows us to solve problems that range from the strictly practical to the highly abstract, to communicate with our fellow human beings through language, to create new ideas and imagine things that have never existed, to feel love and happiness and disappointment, and to experience an awareness of ourselves as individuals. Not only can the brain undertake such a variety of different functions, but it can do more or less all of them simultaneously. How this is achieved is one of the most challenging and exciting problems faced by contemporary science.
It has to be said at the outset that we are completely ignorant of many of the things that the brain does, and of how they are done. Nevertheless, very considerable advances have been made in the neurosciences over the last decade or two, and there is growing confidence among neuroscientists that a real understanding is beginning to emerge. This feeling is encouraged by the increasing integration of the various disciplines involved in neuroscience, and a convergence of both experimental findings and theoretical models.
Neuropsychology, as one of the neurosciences, has grown to be a separate field of specialization within psychology over about the last 40 years, although there has always been an interest in it throughout the 120-year history of modern scientific psychology. Neuropsychology seeks to understand the relationship between the brain and behavior, that is, it attempts to explain the way in which the activity of the brain is expressed in observable behavior. What mechanisms are responsible for human thinking, learning, and emotion, how do these mechanisms operate, and what are the effects of changes in brain states upon human behavior?
There are a variety of ways in which neuropsychologists conduct their investigations into such questions, but the central theme of each is that to understand human behavior we need to understand the human brain. Psychology without any reference to physiology can hardly be complete. The operation of the brain is relevant to human conduct, and the understanding of how the brain relates to behavior may make a significant contribution to understanding how other, more purely psychological, factors operate in directing behavior. Just how the brain deals with intelligent and complex human functions is, in any case, an important subject of investigation in its own right, and one that has immediate relevance for those with brain injuries and diseases, as well as a wider relevance for medical practice.
It would be misleading to suggest that, following its protracted birth, neuropsychology has emerged as an entirely unified discipline. In reality, there remain different emphases among practitioners and researchers, which broadly divide into two domains: those of clinical and cognitive neuropsychology. At the risk of oversimplifying the distinction, the former tends to focus on the effects of brain damage/disease on psychological processes such as memory, language, and attention, and often has a clinical remit for assessment and even treatment. Conversely, the latter tries to understand impairments to psychological processes in terms of disruptions to the information-processing elements involved. In other words, the clinical approach goes from the damaged brain to psychological dysfunction and its remediation, whereas the cognitive approach goes from psychological dysfunction to hypothetical models about the individual stages of information processing that could explain such dysfunctions, which may (or may not) then be “mapped” onto various brain regions. This division has led to quite heated debates among neuropsychologists about, for instance, the merits/shortcomings of single-case versus group research designs, and the extent to which cases of localized brain damage can ever definitively be used as evidence in support of functional localization.
SCOPE OF NEUROPSYCHOLOGY
The intent, of course, is praiseworthy, but many clinical neuropsychologists are very concerned about the actual application of scientific standards in the hands of individuals such as trial judges who, while highly intelligent and astute, are not usually formally trained in science. Future clarification of the Daubert decision in actual court decisions is expected, and the degree to which Daubert achieves its purpose will determine if a lasting contribution is made.
Neuropsychology Assessment Measures and Clinical Neuropsychology
The hallmark of neuropsychological assessment measures has been their careful validation relative to neurological criteria (Horton, 1997b; Reitan, 1974; Reitan & Davison, 1974; Reitan & Wolfson, 1993). There is clear agreement among scientists and researchers as to the impressive empirical validity of neuropsychological tests to determine the presence of brain damage and lateralization of the brain damage (Horton, 1997b). On the other hand, there has been a relative paucity of specific research with neuropsychological tests addressing questions related to ecological validity issues, and the argument has been made that empirical evidence for the ecological validity of neuropsychological tests needs to be much better developed (Sbordone & Saul, 2000). It is to be expected that a future trend will be to address this important area.
Neurodiagnostic Assessment Measures and Clinical Neuropsychology
Neurodiagnostic measures such as magnetic resonance imaging (MRI) and positron emission topography (PET) scanning have provided new windows through which to visualize the human brain (Bigler, Lowry, & Porter, 1997). The expectation is that increased use of these exciting brain imaging techniques will be the norm in clinical neuropsychology. The interactive use of neuropsychological testing and neurodiagnostic measures such as MRI and PET scans might be expected to yield new dramatic insights into the workings of the human brain and further develop the empirical basis for clinical neuropsychology.
Malingering Measures and Clinical Neuropsychology
In the last decade, the most dramatic development in clinical neuropsychology has been the explosive growth of test measures designed to detect biased responses on neuropsychological tests (Franzen & Iverson, 1997). The development of new measures, use of specific profiles, item response patterns, and cut-off scores on standard neuropsychological tests have been investigated. Future research in this area is expected.
Medical/Health Care Patients and Clinical Neuropsychology
In the area of medical neuropsychology (Horton, 1997a) there are many opportunities for clinical neuropsychologists to make important contributions. Patients that have had systemic illnesses that have secondary brain effects (such as lung disease, cardiovascular disorders, liver disease, and selected ontological disorders, among many others), as well as cases where the effects of pharmaceuticals are in question, are clear candidates for clinical neuropsychological assessment to determine if brain damage has occurred. In addition, cases where medical complications or treatment may have a direct or indirect impact on neural integrity and where neurotoxic effects of chemicals/substances are suspected are considered within the possible scope of clinical neuropsychology (Hartman, 1995). In addition, in cases where patients have survived brain injury and now are being rehabilitated, neuropsychologists can be of assistance (Hall & Cope, 1995).
Minority Groups and Clinical Neuropsychology
As the population of the United States grows increasingly more diverse, greater attention to the neuropsychological assessment o minority groups is an inevitable development. The expectation is that appropriate neuropsychological assessment may have to be tailored to fit the cultural context of new immigrants to the United States and those who maintain a different cultural perspective than the majority culture. The extant research on neuropsychological assessment in a multicultural context, however, is actually quite rudimentary (Horton, Carrington, & Lewis-Jack, 2001). When minority group members are neuropsychologically assessed a firm empirical basis for decision making is needed. At present, much additional work is needed to address the area of clinical neuropsychological assessment within a multicultural context.